How Climate Change is Killing Coral Reefs and What You Can Do to Help

Coral reefs are essential to marine ecosystem health, contributing an estimated $2.7 trillion a year in economic activity globally. Yet if global warming exceeds 1.5 degrees Celsius as set by scientists, reefs will vanish entirely.

Photo by Francesco Ungaro

Erosion from coastal development, dredging and mining operations, destructive fishing practices and boat anchors are all threats to coral habitats that stir up sediment that covers them and threatens their resilience.

The Hidden Dangers of Coral Bleaching

Coral reefs are essential to marine biodiversity, providing home for one third of all sea creatures and supporting fisheries that sustain billions of people worldwide. Coral reefs also form the basis of some of nature's greatest wonders such as Australia's Great Barrier Reef which now faces imminent demise due to back-to-back marine heat waves.

Human-caused climate change has led to unprecedented global ocean warming over the last 11,000 years, straining coral polyps and forcing them to expel their host zooxanthellae (or algae) which provides them with vital energy sources to sustain life; when this occurs it is known as coral bleaching; without this energy source the coral would perish as its inhabitants lose vital energy sources that fuel its development and survival.

Bleached corals may not be dead, but they're more stressed and vulnerable to disease than previously. Their offspring also find it harder to disperse because nutrient-rich waters where algae reside are no longer accessible to them. Over time, however, bleached corals may succumb to other threats, including infection from infectious coral diseases.

Apart from climate change, other factors that contribute to coral reef degradation include sea level rise; changes in frequency, intensity and direction of tropical storms; and altered ocean currents. Ocean acidification due to carbon dioxide absorption through fossil fuel combustion also has negative consequences on reef ecosystems by decreasing pH levels in seawater and leading to reduced levels of biodiversity in reef environments.

Scientists analyzed data from 10 coral reef-bearing regions worldwide and determined that coral loss was directly correlated to increasing temperatures; higher temperatures made coral more prone to bleaching. Further investigation revealed deeper shaded reefs were less likely to experience bleaching episodes.

Climate change is the main driver of coral reef decline worldwide and even with immediate emission cuts, the reefs still face substantial challenges. Other threats include pollution from fertilizer use and runoff as well as excess nitrogen levels in the water which disrupt beneficial partnerships between corals and algae by providing too much nitrogen into the environment.

Overfishing

Coral reefs worldwide are suffering due to a combination of local stresses, including overfishing, pollution and pathogenic disease. These threats weaken reefs further making them susceptible to warming ocean temperatures as well as pathogenic disease that exploit stressed environments. A special report by the Intergovernmental Panel on Climate Change released earlier this summer estimated that global average ocean temperatures would increase 1.5 degrees Celsius above pre-industrial levels and that coral reefs may decline 70-90% within 50 years; altogether at 2 degree warming they would disappear completely.

Overfishing destroys marine ecosystems by depriving reef-building coral of key predators or prey species such as large predatory fish such as sharks. As a result, smaller and less important food web components like sardines and anchovies take over and begin dominating reef food webs, leading to disruption of entire food webs as well as changes to habitats for other species. This process also contaminates ocean waters affecting other organisms that inhabit them.

Removing herbivorous fish also disrupts reef ecosystems by upsetting their delicate balance, as these plants play an essential role in clearing away excess algae which could smother coral and lead to its death. Corals with high algae cover are up to six times more susceptible to disease; furthermore, overfishing reduces levels of naturally-produced antibiotics which corals use against bacteria infections.

Reefs require clean water in order to flourish, yet most nearshore pollution comes from land-based sources such as agricultural runoff, industrial waste and urban development. Rivers transport these pollutants directly into coastal regions where they pollute reef waters causing coral bleaching and death as well as an influx of nutrients leading to algal overgrowth.

Education of the public about responsible seafood choices can lead to changes in fishing practices, while marine protected areas provide safe havens from climate change that give coral reefs a chance at survival against rising temperatures. But ultimately reducing greenhouse gas emissions remains the best way to save reefs as coral reefs require stable and cool conditions for their survival.

Debris

Coral reefs can be thought of as "rainforests of the sea", boasting both aesthetic and economic value for coastal communities. Home to thousands of fish species, crustaceans, clams and turtles as well as humans providing food, protection from storms and regulation of ocean climate - they're an integral component of coastal environments and should not be underestimated!

Reefs are in peril. Since 2009, global warming has helped eradicate 14 percent of world coral populations, according to scientists who warn that if we continue on this course they could all but vanish within this century.

Rising ocean temperatures put coral at risk of bleaching, an environmental phenomenon in which their relationship with algae becomes too intense to bear and they exppel it en masse, turning their polyps white in color and expelled by their expulsion glands. Bleaching corals don't die immediately but remain susceptible to disease and starvation.

Coral reef decline can also be contributed to by many other environmental factors, including agricultural fertilizer run-off contaminating the water (and then coral), storms that disturb manure lagoons, industrial pollution and household waste, among many others. When too much phosphorus and nitrate enters the ocean it leads to toxic algal blooms that smother coral.

Other reef-disrupting pollutants include oil, gasoline and plastics. When these contaminant reach coral reefs, they clog pores and hinder their ability to breathe or digest food efficiently.

There are steps we all can take to help keep reefs healthy and vibrant, including recycling and practicing the three R's of reduction, reuse and recycling (reduce, reuse and recycle). Another easy conservation action is participating in beach cleanups both your own and others'. Trash left on beaches harms corals and marine life as well as pollutes local and national waterways; also be sure to learn safe boating around reefs so anchors or chains don't damage them and be an advocate for sustainability among your friends and family.

Climate Change

Coral reefs around the world have lost 14% of their surface area over just 10 years, and further decline will occur if ocean temperatures keep increasing. Overfishing, pollution and reckless tourist activities all play their role; however, global warming and ocean acidification pose the greatest threats.

The oceans absorb an estimated 22 million tons of carbon dioxide each day, altering water chemistry and increasing acidification. This makes it harder for corals to build their protective skeletons as less calcium carbonate remains in the ocean water for use by corals to form hard protective shells; contributing significantly to recent mass bleaching events that have decimated some reefs.

Warmer waters can also influence tropical storm frequency and intensity, and compound problems caused by sediment runoff, nutrient enrichment and algae blooms. Although scientists have tried to help corals adapt, many reefs won't survive without further assistance from human efforts.

A report released this week by the Global Coral Reef Monitoring Network revealed that global reefs were under attack from multiple stressors -- such as sea surface temperature, ocean acidification, coral bleaching and land use. Researchers calculated that by 2055 93% of reefs will have become inaccessible due to these five stressors and projection scenarios resulting from them were used by researchers in modeling and projection scenarios.

But scientists behind a new study hope to extend corals' lives by identifying areas with more resilient environments - whether due to upwelling of cooler waters or strong currents. Furthermore, they aim to understand what characteristics allow certain corals to withstand extreme conditions and share that knowledge across other reefs.

Not only can we all do our part by protecting coral reefs and expanding marine protected areas, but we can all also take steps to lower our carbon footprints. Switching to cleaner transportation options, supporting sustainable brands, eating more plant-based foods and recycling plastic can all contribute towards cutting greenhouse gas emissions. You can even help by limiting single-use plastic usage or recycling what plastic you do use!

Speak to your friends and family about coral reefs - the "rainforest of the sea". Encourage them to learn more, while writing to your lawmakers demanding action such as restricting sewage discharge to the ocean, expanding marine protected areas, or counteracting climate change.